1. Field of the Invention
The present invention relates to a photoreceptor belt drive system for an image transfer apparatus and, more particularly, to a photoreceptor belt drive system with steerable capstans.
2. Prior Art
Conventional electro photographic image transfer apparatus, such as printer, include a photoreceptor member and a drive or transport system for transporting the photoreceptor member through various processing stations in order to generate an image on the photoreceptor member. The transport system controls the speed of the photoreceptor member as it moves through the multiple processing stations of the electro-photographic printer so that all image bearing sections on the photoreceptor are correctly orchestrated with the various processing stations, and each station processes an appropriate section of the photoreceptor. For example, in color printers where multiple latent images are separately developed on the photoreceptor member using different color toners and are then transferred to a common surface, the quality of the final image is dependent on how accurately each of the latent images is placed or registered on the photoreceptor. As is well known, when separate color images are superimposed to form a full-color image, slight misregistration of the individual colors may cause undesirable features to appear that render the final output unacceptable to a user. Registration problems may manifest themselves through image defects. For example, color fringes surrounding sharp edges within the image proper, or xe2x80x9cmoire fringesxe2x80x9d or xe2x80x9cbandingxe2x80x9d result in visible spatial interference patterns distributed throughout the image. Precise placement of pixels of the latent images on the photoreceptor member, both in a process direction within the apparatus, and in a direction transverse (i.e. lateral, or cross-process direction) to the process direction aids in avoiding these defects in the output image. The accuracy of the placement of the latent images may be affected by factors such as imperfections or distortions in the system geometry of both the photoreceptor member and of the processing stations, and how precisely the transport system itself controls the speed of all image bearing sections of the photoreceptor member. By way of example, the photoreceptor member may be disposed such that its photoreceptor surface is angled or tilted relative to a true position in which the surface is to move through a processing station. This distortion alters both the lateral placement and speed of the photoreceptor surface with respect to the processing station. Improper placement and speed of the photoreceptor causes inaccurate placement of the latent image on the photoreceptor thereby leading to imperfection in the final output image as previously described. In the cases where the photoreceptor is a continuous loop belt, conventional systems for controlling photoreceptor belt lateral movement fall in two categories: passive alignment systems which make use of physical contact with the edge of the belt for alignment thereof; and active alignment systems utilizing active driving arrangements to alter the direction of travel of the belt. Existing passive alignment systems for controlling belt lateral movement generally comprise crowned or flanged rollers. Frequently, high local stresses are produced on the belt edges by flanged devices resulting in undue wear and buckling of the edges of the highly sensitive photoconductive belt. Active systems, on the other hand, are generally characterized by servo systems employing steering rollers. Servo systems generally apply less stress to the side edges of a belt, but incorporate more sophisticated and expensive hardware. Movement of the steering rollers may also cause physical distortion and other undesirable disturbances in the photo receptor belt at the imaging stations. The present invention overcomes the problems of the prior art as will be described in greater detail below.
In accordance with a first embodiment of the present invention, a transport system for transporting sheet media in an image transfer apparatus is provided. The transport system comprises a drive section, and at least one wheel drivingly connected to the drive section. The at least one wheel is disposed to contact the sheet media. The at least one wheel transports the sheet media generally in a process direction in the image transfer apparatus when the at least one wheel is driven by the drive section. The at least one wheel is steerable for orienting the axis of rotation of the at least one wheel in a predetermined direction, and for controlling a direction of travel of the sheet media relative to the process direction.
In accordance with a second embodiment of the present invention, an image transfer apparatus is provided. The image transfer apparatus comprises a frame, at least one imager, an image process station, and a transport system. The imager is supported by the frame for generating an image on a photoreceptor media. The image process station is supported by the frame for processing the image on the photoreceptor media. The transport system is mounted to the frame for transporting the photoreceptor media in a process direction between the imager and the image process station. The transport system is adapted for forming a slack section in the photoreceptor media between the imager and the image process station. The transport system comprises a pair of wheels which contact the photoreceptor media at the imager, and transport the photoreceptor media when the pair of wheels are rotated about their respective axes. Each of the transport wheels is pivotably mounted to the frame so that each transport wheel is pivotable relative to the frame about a corresponding pivot axis. The pair of transport wheels are pivoted relative to the frame for translating the photoreceptor media at one end of the slack section in a direction incrementally transverse to the process direction.
In accordance with a third embodiment of the present invention, an electro-photographic image transfer apparatus is provided. The image transfer apparatus comprises a frame, at least one imager, at least one developer, at least one fuser, and a transport system. The imager is connected to the frame for forming a latent image on a photoreceptor media. The developer is connected to the frame for developing the image on the photoreceptor media. The fuser is connected to the frame for transferring the image on the photoreceptor media to a final media. The transport system is mounted to the frame for transporting the photoreceptor media in a process direction to at least one of the imager, the developer, or the fuser, wherein the transport system comprises a pair of capstan wheels which propel the photoreceptor media in the process direction when the capstan wheels are rotated about their respective axes of rotation. Each wheel of the pair of capstan wheels is pivotably mounted to the frame so that each capstan wheel is pivotable about a corresponding pivot axis relative to the frame.
In accordance with a method of the present invention, a method for forming an image with an electro-photographic image transfer apparatus is provided. The method comprises the steps of providing the image transfer apparatus with an imager, providing the image transfer apparatus with a transport system, and pivoting a pair of wheels. The image transfer apparatus is provided with an imager for forming an image on a photoreceptor belt. The image transfer apparatus is provided with a transport system for moving the photoreceptor belt in a process direction. The transport system moves the photoreceptor belt in the process direction past the imager. The transport system is provided with at least one pair of wheels which propel an independent section of the photoreceptor belt. Each wheel of the pair of wheels is hinged to pivot about a corresponding pivot axis relative to the process direction. The pair of wheels pivot relative to the process direction to propel at least a portion of the photoreceptor belt in a vector direction incrementally transverse to the general process direction.